This invention pertains to lubricants and, more particularly, to a lubricating grease which is particularly useful for drive joints of front-wheel drive vehicles.
In front-wheel drive automobiles, vans, and trucks, the front wheels are driven by the engine via a front axle assembly and a number of front-wheel drive joints. These front-wheel drive joints facilitate movement of the front axle assembly while maintaining constant rotational velocity between the front wheels. The front-wheel drive joint is often referred to as a constant velocity (CV) joint. The outer CV joint usually has a boot comprising an elastomer, such as polyester or neoprene, and the inner joint usually has a boot comprising a higher temperature-resistant elastomer, such as silicon-based elastomers.
Front-wheel drive joints experience extreme pressures, torques, and loads during use. Operating temperatures can vary from -40.degree. F. during winter to over 300.degree. F. during summer.
Front-wheel drive greases are required to provide wear resistance. When a front-wheel drive vehicle is driven, sliding, rotational, and oscillatory (fretting) motions simultaneously occur within the front wheel drive joint, along with large loads and torques. A grease which minimizes wear from one of these motions or conditions will not necessarily protect against the others.
With the newer designs of many automobiles, trucks, vans, and other mobile equipment, the extreme pressure and wear resistance properties of the front-wheel drive grease have steadily increased. Previous additive technologies which give levels of performance typified by prior art greases may no longer be satisfactory for truly outstanding performance. Higher levels of performance are desired.
Front-wheel drive greases are also required to be chemically compatible with the elastomers and seals in front-wheel drive joints. Such greases should not chemically corrode, deform, or degrade the elastomers and seals which could cause swelling, hardening, loss of tensile strength, and ultimately rupture, oil leakage, and mechanical failure of the CV joints and seals.
Another requirement of front-wheel drive greases is that the grease and all its components be non-reactive, and non-corrosive to ferrous and non-ferrous metals even when prolonged contact occurs at high temperatures. The importance of this is readily apparent in applications such as front-wheel drive joint lubrication where temperatures in excess of 300.degree. F. can occur and the grease must perform for the entire life of the joint. If the lubricant or any component therein becomes corrosive to the steel parts, such corrosion will result in accelerated wear and ultimate failure of the joint. Similarly, if any component of the grease reacts with water to form corrosive compounds, similar premature joint failure will result. This latter effect can be particularly troublesome since small amounts of moisture will usually be present in the joint due to the ambient humidity of the air.
Another requirement of front-wheel drive greases is that they should be toxicologically safe. During the assembly line filling of CV joints with front-wheel drive grease, workers can be exposed to the lubricant. Also, the front-wheel drive grease used by CV joint manufacturers is also often used in CV joint repair kits which are sold in various automotive parts retail stores. These kits are sold to members of the general public who wish to repair or replace a CV joint or CV joint boot on their car. The grease in such kits is generally stored in a plastic pouch. Persons using such kits will invariably come in contact with the grease during the act of opening the pouch and applying the grease to the CV joint. Therefore, front-wheel drive grease should contain no materials which are severe skin irritants. Moreover, front-wheel drive grease should contain no materials which are carcinogenic or mutagenic. Neither should front wheel drive greases contain materials which are members of the same chemical family of similar materials which have been shown to be carcinogenic or mutagenic.
Over the years, a variety of greases and processes have been suggested for use with front-wheel drive joints and/or other mechanisms. Typifying such greases and processes are those found in U.S. Pat. Nos. 2,964,475; 2,967,151; 3,259,573; 3,344,065; 3,843,528; 3,846,314; 3,920,571; 4,107,058; 4,305,831; 4,431,552; 4,440,658; 4,514,312; 4,759,859; 4,787,992; 4,830,767; 4,859,352; 4,879,054; 4,902,435; and Re. 31,611. These greases have met with varying degrees of success but most do not meet all the requirements described above.
In particular, U.S. Pat. No. 3,259,573 does not provide the higher level of performance required in todays more highly loaded CV joints and other similarly loaded parts.
U.S. Pat. Nos. 4,107,058, 4,305,831, and 4,431,552 do not provide compositions with non-corrosivity to elastomers, ferrous metals and non-ferrous metals at prolonged high temperatures due to their required inclusion of organo-sulfur materials.
U.S. Pat. No. Re 31,611 requires the use of materials which are very corrosive to ferrous and non-ferrous metals at high temperatures. Furthermore, this corrosive action dramatically accelerates the rusting of ferrous metals if even very low levels of moisture are present. Also, these materials are members of a family of compounds which have been found to exhibit carcinogenic characteristics, to be of limited solubility in mineral oil, or both.
It is, therefore, desirable to provide an improved extreme pressure and wear-resistant grease which overcomes most, if not all, of the above problems.